Aqueous emulsion explosives of the water-in-oil type are well known, as in U.S. Pat. Nos. 3,161,551; 3,164,503 and 3,447,978. U.S. Pat No. 4,248,644 teaches non-aqueous melt-in-fuel emulsion technology wherein essentially anhydrous molten salts are emulsified with an immiscible hydrocarbon fuel. The hydrocarbon fuel forms the continuous phase and the molten oxidizer forms the discontinuous phase. A fuel-continuous emulsion in obtained which is grease-like or extrudable at ambient temperatures.
Until recently, developments in non-aqueous melt-in-fuel emulsion explosives have been directed toward soft or pumpable explosives for commercial blasting operations. However, U.S. patent applications Ser. Nos. 578,177; 578,178; 578,179; 597,415 and 597,416 teach unstable melt-in-fuel emulsions which are castable. These emulsions are formulated so as to be unstable; that is, when cooled, the continuous phase is disrupted as the discontinuous droplets of molten oxidizer crystallize and knit together, forming a rigid structure.
Such compositions derived from unstable emulsions suffer from several disadvantages: The carefully regulated intimacy of fuel and oxidizer mixing achieved during process refinement is subject to the disruptive effects of oxidizer crystal growth and interknitting with potentially adverse effects on performance, sensitivity and storage life of the product. Further, the disruption of the fuel continuum increases the exposure of the oxidizer salts to the effect of moisture which also adversely affects both storage life and performance.
It has not been apparent heretofore that castable energetic compositions can be made from stable non-aqueous emulsions which retain oxidizer phase discontinuity during solidification of the individual oxidizer cells. In contrast to cast compositions made from unstable emulsions, the compositions of the present invention become solid, rigid or firm following cooling without significant disruption of the fuel phase continuum or substantial interknitting of the separate oxidizer cells. As expolsives, the shear sensitivity of the compositions may be reduced and the safety enhanced through internal lubrication by the fuel continuum. As propellants, elastomeric properties may be achieved superior to those of compositions exhibiting the more brittle, interknit crystalline structure resulting from unstable emulsions. In all such castable compositions made from stable emulsions, whether explosives, propellants, flares or gas generators, a high degree of fuel and oxidizer intimacy is maintained on solidification; and superior water resistance and shelf life result from preservation of the fuel continuum.
It is the principal objective of this invention to obtain solid, rigid or firm energetic compositions from stabe non-aqueous emulsions such that the fuel continuous geometry and intimacy of ingredients characteristic of the fluid emulsion is maintained in the final solid product. It is another objective to formulate the compositions in a manner which will permit continuous processing, cooling, optional admixing of additives, and loading or packaging, before solidification. Another objective is to achieve supercooling to or near to ambient temperatures before solidification in order to reduce cast defects resulting from thermal shrinkage. A further objective is to achieve water resistance in the compositions. Other objectives are to achieve internal lubrication and reduced shear sensitivity in explosive compositions and substantially to prevent interknitting of oxidizer crystals so as to achieve improved elastomeric properties in propellants and plastic bonded explosives.
Because the oxidizer cells in the final product are typically sub-micron in certain dimensions, the products are referred to as microcellular composite energetic materials.
Since the discontinuous phase of the fluid emulsion as first formed remains substantially discontinuous in the final solidified product, and since the continuous phase remains substantially continuous in the final solidified product, microcellular composite formulations can also be referred to as solid emulsions. This term is intended to include those microcellular formulations which have solidified as a result of either or both phases having become solid.